Bistable command module



Aug- 20, 1968 J. s. POOLE 3598330 B I STABLE COMMAND MODULE Filed April 25, 1965 2 Sheets-Sheet 1 coMMAND TR'GGER lNPuT 2 INVENTOR JOHN 5. POOLE BY W ATTORNEY Aug. 20, 1968 Filed April 23, 1985 G) GOMMAND TRIGGER PULSE (b) SCR (0) GAPACITOR 22 (d GAPAOITOR 27 (e) POSITION OF RELAY CONTACT 28 J. s. PooLE BISTABLE COMMAND MODULE oFF CHARGED DISCHRGEDI CHARGED 2 Sheets-Sheet 2 DISCHARGED TERMlNAL 17| TERMINAL 23 INVENT OR JOHN S. POOLE ATTORNEY United States Patent O 3,398,330 BISTABLE COMMAND MODULE John S. Poole, Oxon Hill, Md., assignor to the United States of America as represented by the Secretary of the Navy Filed Apr. 23, 1965, Ser. No. 450,552 5 Claims. (Cl. 317-1485) ABSTRACT OF THE DISCLOSURE A bistable gating circuit including a pair of parallel circuits having their common connection coupled to a single silicon-controlled-rectifier control element. A conventional magnetic latching relay having two coils is employed, with each coil connected in one of the two parallel networks, `and a relay contact, controlled by either of the coils, couples a voltage source to a storage means in one or the other of the parallel networks. This bistable command circuit is utilized for switching a voltage source to one of several loads and requires only a single gating means and a single control input.

` The invention ldescribed heren may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to bistable electronic circuits and in particular to a bistable gating circuit controlled by a single input suitable for use in space Vehicles.

Those concerned with the development of command circuits for use in satellite instrumentation have long recognized the need for a simple and reliable means for applying power to one or more loads by changing the state of a latching relay while utilizing a minimum of components, power and signal requirements, and employing but a single gating means which is triggerable by a single input. Conventionally, a latching relay is employed having two coils with a source of voltage switched to either one coil or the other. This requires two drive elements, one for each coil. Independent control signals are also required for each drive element. In such circuts, the system draws a large current which is limited only by the coil resistance whenever the drive element remains ON or a component fails. In the case of satellite instrumentation where power is severely limited, this could prove disastrous. Prior art circuits usually require a large number of components including several semiconductor elements and more than one gating means for energizing the relay coils. Another disadvantage is that those circuits usually require standby power. i

' The general purpose of this invention is to provide a bistable command circuit which embraces all the advantages of similarly employed circuits and possesses none of the aforesaid disadvantages. To attan this, the present invention 7contemplates a unique bistable circuit comprising a pair of parallel circuits having their common connection coupled to a single silicon-controlled-rectifier control element. A conventional magnetic latching relay having two coils is employed, with each coil connected in one of the two parallel networks. A relay contact, controlled by either of the coils, couples a voltage sources to a storage means in one or the other of the parallel networks through a current limiting resistor in its respective network. A unidirectional device is provided in each network for preventing the charging of both storage means simultaneously and is serially connected with the relay coil and the current limiting resistor of its respective network.

The circuit of this invention requires a minimum of components including only three active components, two

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of which are diodes, and the other of which is a siliconcontrolled-rectifier (SCR). The 'circuit may be Controlled by several microwatts of power and can switch many watts of power. Only a single control input is needed and the control signal waveform is not critical. The only requirement of the input trigger signal is that it possess suflicient power to turn on the SCR gate. Another important feature is that in the case of component failure the only power consumed is that of the limiting resistor. In satellite applications, such failure results only in the loss of the command function rather than the loss of the entire payload.

' An object of the present invention is to provide a sim ple and reliable bistable circuit having a minimum number of components.

Another object is to provide a simple and reliable bistable circuit having a minimum number of components and requiring a minimum amount of power and-no standby power.

A further object is to provide a bistable command circuit for switching a voltage source to a load and requiring only a single gating means and a single control input.

Still another object is to provide a bistable command circuit suitable for satellite applications wherein the payload may be protected if a component fails.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 illustrates an embodiment of the bistable command circuit of the present invention; and

FIG. 2 is a series of timing diagrams, (a) through (e), for illustrating the time relationship of pulses in the circuit of FIG. 1.

Referring now to the drawings, there is shown in FIG. 1 a bistable command circuit having an input terminal 11 for receiving a command signal and input resistor 12 connected across the input for developing a signal which is applied to the gate of silicon-controlled-rectifier (SCR) switch 13 for triggering the SCR. The cathode of the SCR is connected to ground while the anode is coupled to two parallel networks 14 and 15. Network 14 comprises a relay terminal 17, resistor 18, coil 19 of a magnetic latching relay and diode 21, all serially connected together. Storage capacitor 22 is connected from a point common to resistor 18 and relay coil 19 to ground. Network 15 is identical to network 14 and comprises relay terminal 23, resistor 24, coil 25 of the magnetic latching relay, and diode 26 serially connected together. Storage capacitor 27 is connected from a point common to resistor 24 and -relay coil 25 to ground. A voltage source is connected to either network 14 or 15 through relay contact 28 which is applied to either relay terminal 17 or relay terminal 23. Also connected to terminals 17 and 23 are loads 31 and 32, respectively.

FIG. 2 illustrates a series of timing diagrams, (a) through (e), which are useful in describing the operation of the circuit of FIG. 1. In operation, the capacitor connected to the charging source will charge in accordance with the time constant defined by the product of its capacitance value and the value of limiting resistance. With does not appear at terminal 23. When a command trigger pulse of FIG. 2(a) is applied .at a time t1 to the command trigger input 11, the SCR is turned ON as shown in FIG. 2(b) and capacitor 22 discharges, as shown in FIG. 2(c), through coil 19, thereby causing relay contact 28 to switch from relay terminal 17 to relay terminal 23 as shown in FIG. 2(e), so that the voltage source is applied to capacitor 27 through limiting resistor 24. The SCR remains ON until the anode current decreases below the holding value at a time tz at which time it will switch OFF as shown in FIG. 2(b), and capacitor 27 then charges toward the supply voltage as shown in FIG. 2(d). The anode of the SCR rises with the same time constant as that of the charging capacitor 27. The current limiting resistor 18 must be suflicient to limit the current through the SCR below the `anode holding value in the absence of capacitor discharge. Diode 21 blocks capacitor 22 from the voltage source while capacitor 27 is being charged.

When contact 28 is switched to terminal 23, coil 25 is not energized since current initially fiows through resistor 24 to a path through uncharged capacitor 27, and also since current limiting resistor 24 is chosen so Athat current through the coil is limited to a level which is insufficient to energize the relay coil. In order to energize a c-oil, the added current from the storage capacitor is necessary. Since both networks are identical, the same explanation applies when contact 28 is switched to terminal 17.

The above operation is repeated and relay contact 28 switches to the opposite relay terminal upon the receipt of each command trigger pulse. Consequently, relay contact 28 will be alternately applied to terminals 17 and 23 as illustrated in FIG. 2(e) upon the receipt of each consecutive command pulse by the SCR gate. Since a load to be energized by a voltage source may be connected to either or both of the terminals 17 and 23, the circuit may be used to alternately energize two loads (31 and 32 of FIG. 1) upon receipt of a command pulse, or to energize a single load upon receipt of each alternate command pulse. In the latter case, a single load is turned ON and OFF by consecutive command pulses. .V

Various contact switching configuratons are within the scope of this invention depending on the number of relay contacts required. The only limitation is that one contact must be used to apply the voltage source to the circuit so that the advantage of requiring no standby power is retained. For the particular set of contacts applying v-oltage to the circuit, the circuit of this invention and a particular load will be connected in parallel so that the same voltage source which supplies power to the circuit also supplies power to the load.

In Summary, the present invention provides a bistable switching circuit requiring no standby power and having a minimum number of components including a single control element with a single input. Power for operation of the circuit is obtained from the voltage source which is to be switched and applied to a particular load. The circuit is especially useful in satellite instrumentation where available power and space are lirnited and where payload protection in the event of component failure is a prime consideration. Application of the invention need not be limited to satellite instrumentation since there are countless other environments requiring the particular advantages and features of this invention.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. For example, any suitable control elements may be employed for the SCR switch. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. A bistable command circuit comprising:

a pair of networks;

storage means in each network;

means operatively associated with said storage means for chargin'g either of said storage means;

a trigger input;

gating means common to both networks for discharging said storage means upon receipt of a command pulse wherein said gating means includes a single silicon-controlled-rectifier having its anode coupled to ground, and its gate input coupled to save trigger input; and

inductive means in each of said networks operatively associated with a respective one of said storage means and responsive t-o the discharging of the storage means in its respective network so as to switch said charging means to the other of said networks so as to enable the charging of said storage means in said other network.

2. A bistable command circuit as set forth in claim 1 further including a pair of -unidirectional elements with each unidirectional element coupled between the anode of said silicon-controlled-rectifier and one of said inductive means for allowing said storage means to discharge only through a unidirectional element and the inductive means of its respective net-work and through said gating means when said gating means is triggered.

3. A bistable command circuit as set forth in claim 1 further comprising a current limiting means, coupled between said storage means in each network and said charging means, for limiting the current from said charging means.

4. A bistable command circuit comprising:

a trigger input for receiving a command pulse;

first and second parallel networks, each network comprising a relay terminal, a limiting resistor, a relay coil, and a diode, all serially connected, and a capacitor coupled from a point com-mon to said limiting resistor and said relay coil to ground;

switching means having a control element coupled to said trigger input, said switching means connected in a current path common to said first and second parallel networks;

a voltage source; and

a relay contact Controlled lby said relay coil in each of said first and second networks to be selectively coupled between said voltage source and said relay terminal of one of said networks;

whereby a capacitor in said first network charges through its respective limiting resistor when a voltage is applied vby said relay contact to the relay terminal of said first network, and whereby said capacitor discharges through said relay coil and said diode of said first network and through said switching means when said control element of said switching means is triggered by said command pulse, thereby applying said relay contact to the terminal of said second network.

5. The bistable command circuit of claim 4 wherein said switching means comprises a single Silicon-controlled-rectifier having its anode coupled to a point common to the diodes in each of said networks, its cathode coupled to ground, and its gate coupled to said trigger input.

References Cited UNITED STATES PATENTS 2,\692,963 10/ 1954 Hathaway 307-41 XR 2,954,512 9/1960 Hardison 317-151 3,l82,222 5/1965 Lacy et al. 317-1485 3,189,794 6/ 1'965 Currie, Jr. 317- ROBERT K. SCHAEFER, Primary Examiner.

ORIS L. RADER, Examiner.

T. B. IOIKE, Assistant Examiner. 

